Liquid crystal display element, and use of phase difference film used the same for

ABSTRACT

The present invention provides a liquid crystal display device of VA mode having decreased leakage of light over a wide range and giving a clear and almost achromatic black display by using a retardation film A having smaller retardation with shorter wavelength in combination with a retardation film C having larger retardation with shorter wavelength. Accordingly, a high-quality liquid crystal display device having excellent picture quality can be produced by the present invention.

TECHNICAL FIELD

[0001] The present invention relates to a liquid crystal display deviceof vertical orientation mode to orient the major axis of the liquidcrystal molecule nearly perpendicular to the panel face the liquidcrystal cell in a state free from the application of voltage.

BACKGROUND TECHNOLOGY

[0002] Liquid crystal display device is generally composed mainly of aliquid crystal cell having a liquid crystal layer sandwiched between apair of substrates, a retardation film and a pair of polarizing filmsarranged perpendicular to each other and placed at both sides of theliquid crystal cell. Liquid crystal display devices have been used inwide fields from small-sized instruments such as watch and electroniccalculator to large-sized instruments such as monitor and televisionset. Elements of TN (Twisted Nematic) mode to use a liquid crystalmolecule having positive dielectric anisotropy were the mainstream insuch liquid crystal display devices. In a TN-mode liquid crystal displaydevice, the orientation direction of the liquid crystal moleculeadjacent to one substrate is twisted by about 90° relative to theorientation direction of the liquid crystal molecule adjacent to theother substrate in a state free from the application of voltage.

[0003] Various developments were performed on the TN-mode liquid crystaldisplay devices for realizing good black display and high contrast. Itis necessary in the TN mode to display the black color under theapplication of voltage, i.e. orient the major axis of the liquid crystalmolecule in the direction nearly perpendicular to the panel face.However, since the liquid crystal molecule adjacent to a liquid crystalpanel substrate keeps horizontal orientation in the TN mode even underthe application of voltage, the polarized state of light varies by thebirefringence of the liquid crystal molecule. Consequently, completeblack color cannot be displayed even by viewing the panel fromperpendicular direction to make the realization of high contrastdifficult.

[0004] On the contrary, in a liquid crystal display device of verticalorientation mode, so-called VA (vertical aligned) mode, the major axisof a liquid crystal molecule is oriented nearly perpendicular to thepanel face in a state free from the application of voltage between apair of substrates constituting the liquid crystal panel. In thevertical aligned mode, the liquid crystal molecule adjacent to theliquid crystal panel substrate also takes a nearly perpendicularorientation relative to the panel face and, accordingly, thepolarization state of the light is scarcely varied by the transmissionof the light through a liquid crystal layer. Consequently, a nearlycomplete black display superior to TN mode usually becomes possible torealize high contrast when the cell is viewed perpendicular to thesubstrate.

[0005] Various techniques have been proposed for improving the viewangle of conventional VA mode display. For example, the specification ofthe JP-A 11-95208 (hereunder JP-A means “Japanese Unexamined PatentPublication) describes a vertical aligned nematic liquid crystal displaydevice composed of a liquid crystal cell, a pair of polarizing filmsplaced above and below the liquid crystal cell in a state directing theabsorbing axes of the films perpendicular to each other, and aretardation film for the compensation of view angle composed of one ortwo retardation films placed between the liquid crystal cell and atleast one of the polarizing films. Concretely disclosed technique is theuse of one retardation film or two laminated retardation films placedbetween the liquid crystal cell and one of the polarizing films (referto the claim 1 and the Examples 1 to 4 (sections 0030 to 0034).

[0006] The specification of JP-A 2000-131693 discloses a VA-mode liquidcrystal display device produced by inserting a specific biaxialretardation film between a substrate and a polarizing film in a mannerto direct the slow axis in the plane of the retardation film to benearly parallel or perpendicular to the absorption axis of saidpolarizing film placed at the side of the retardation film relative tothe liquid crystal layer. Concretely, a lamination of two specificretardation films (refer to section 0064, FIG. 54) or two specificretardation films placed at both sides of a liquid crystal cell (section0070, FIG. 60) are described in the specification.

[0007] However, the VA mode liquid crystal display devices described inthese specifications were successful for the improvement of the viewangle characteristics only at a specific wavelength. In other words, thetransmission of the light of a specific wavelength is decreased byslantly viewing the liquid crystal display device displaying black colorresulting in the widening of the view angle. However, a problem of thecoloring of black color owing to the leakage of light occurs in thesecases when the wavelength of the light is different from the specificwavelength.

[0008] The main object of the invention is to provide a new liquidcrystal display device of VA mode.

[0009] Another object of the invention is to provide a VA mode liquidcrystal display device causing little leakage of light over the wholevisible light range in the case of displaying black color and enablingthe display of nearly achromatic black color.

[0010] A further object of the invention is to provide a new method forsuppressing the light leakage over the whole visible light range toenable the display of nearly achromatic black color by using aretardation film in a VA mode liquid crystal display device in the caseof displaying black color.

[0011] Still further objects and advantages of the invention will becomeapparent from the following explanation.

DISCLOSURE OF THE INVENTION

[0012] The inventors of the present invention have found that theproblem of the coloring of black color by the light leakage is dependenton the wavelength dispersion of the transmission light and supposed thatthe above problem is caused by the use of a retardation film capable ofimproving the view angle characteristics only at a specific wavelengthresulting in the leakage of light at different wavelengths. Based on theabove conception, the inventors of the present invention have paidattention to the wavelength dispersion characteristics of theretardation in the retardation film, and the present invention have beenaccomplished by the finding that the control of the wavelengthdispersion characteristics is important and that the combined use of aplurality of specific retardation films is effective.

[0013] According to the present invention, the objects and advantages ofthe present invention are achieved by a liquid crystal display devicecomposed of a liquid crystal cell having a pair of substrates and aliquid crystal sandwiched between the substrates and orienting the majoraxis of the liquid crystal molecule nearly perpendicular to the face ofthe substrate in a state free from the application of voltage, a 1st anda 2nd polarizing films placed at both sides of the liquid crystal celland having polarizing axes nearly perpendicular to each other and atleast two retardation films (A,C) placed between the liquid crystal celland the 1st and 2nd polarizing films, wherein the retardation film Asatisfies the following formula (1) and/or (2)

R(λ₁)/R(λ₂)<1   (1)

K(λ₁)/K(λ₂)<1   (2)

[0014] in the formulas (1) and (2), R(λ₁) and R(λ₂) are each an in-planeretardation at wavelength of λ₁ and λ₂ and K(λ₁) and K(λ₂) are each aretardation in the direction of the thickness of the retardation film atwavelength of λ₁ and λ₂, and λ₁ and λ₂ are wavelengths satisfying theformula 400 nm<λ₁<λ₂<700 nm, and the retardation film C satisfies thefollowing formulas (3) and (4)

n_(x)≧n_(y)>n_(z)   (3)

1<K(λ ₁)/K(λ₂)   (4)

[0015] in the formulas, n_(x) is the maximum refractive index in theplane of the retardation film, n_(y) is the refractive index in thedirection perpendicular to the direction of the maximum refractive indexin the plane of the retardation film and n_(z) is the refractive indexin the normal line direction of the retardation film, and thedefinitions of K, λ₁ and λ₂ are same as those described above.

BRIEF EXPLANATION OF DRAWINGS

[0016]FIG. 1 is an example of the constitution of the liquid crystaldisplay device of the present invention.

[0017]FIG. 2 is an example of the constitution of the liquid crystaldisplay device of the present invention.

[0018]FIG. 3 is an example of the constitution of the liquid crystaldisplay device of the present invention.

[0019]FIG. 4 is an example of the constitution of the liquid crystaldisplay device of the present invention.

[0020]FIG. 5 is an example of the constitution of the liquid crystaldisplay device of the present invention.

[0021]FIG. 6 is an example of the constitution of the liquid crystaldisplay device of the present invention.

EXPLANATION OF THE SIGNS

[0022]1P: The first polarizing film

[0023] A: The retardation film A

[0024] L: The VA liquid crystal cell

[0025] C: The retardation film C

[0026]2P: The second polarizing film

[0027] B: Backlight

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] The liquid crystal cell of vertical aligned mode (a VA modeliquid crystal cell) of the present invention has a structure holding apair of substrates each having an electrode and placed opposite to eachother interposing a definite distance therebetween provided that atleast one of the substrate with electrode is transparent and holdingliquid crystal molecules between the substrates directing the major axisof the molecule in a direction nearly perpendicular to the substrate ina state free from the application of voltage. The orientation in anearly perpendicular direction means that the average value of theangles between the substrate and the major axis of the liquid crystalmolecules at the displaying pixel is nearly perpendicular, generally 80degrees or more, more preferably 85 degrees or more and furtherpreferably 87 degrees or more. The liquid crystal may be orientedparallel to the substrate at a part other than the displaying pixel in astate free from the application of voltage as disclosed in JP-A2001-235750.

[0029] A phenomenon of the failure in getting uniform display takesplace in a liquid crystal cell of VA mode by the inclination of liquidcrystal molecules in various azimuthal directions under the applicationof voltage to randomly form discontinuous orientation parts, so-calleddiscrenation, simply by perpendicularly orienting the liquid crystalbetween parallel substrates. Various studies have been made on thediscrenation phenomenon. There are reports to control the inclinationangle of the liquid crystal molecule under the application of voltage byforming protrusions on the substrate as described in SID98DIGEST, (1998)p.1081 “A Wide Viewing Angle Polymer Stabilized Homeotropic Aligned LCD”and Display 99 Late newspapers, (1999) p.31 “A Wide Viewing Angle BackSide Exposure MVA TFT LCD with Novel Structure and Process” or forming awindow on the pixel electrode as described in JP-A 7-199190. A reverseTN system is also proposed in the Sharp Technical Journal No.80, 2001.8,p.11 “Development of ASV-LCD Using Continuous Pinwheel Alignment (CPA)mode” in which the liquid crystal molecule is fallen under twisting inthe application of voltage by adding a chiral material to the liquidcrystal. As stated above, there are many orientation states of liquidcrystal of a liquid crystal cell of vertical aligned mode under theapplication of voltage, however, the present invention is not restrictedby the orientation state of the liquid crystal under the application ofvoltage.

[0030] The retardation along the thickness direction of a liquid crystalcell at 550 nm wavelength (hereinafter referred to as K(550)) is usuallyset to be fallen within the range of from −400 nm to −200 nm orthereabout for example in a transmission-type liquid crystal displaydevice. The retardation along the thickness direction is defined by theproduct of the distance of the substrates holding the liquid crystal andthe refractive index anisotropy of the liquid crystal perpendicular tothe substrate.

[0031] The liquid crystal display device of the present invention, forexample a transmission-type liquid crystal display device is usuallyprovided with a backlight at the side reverse to the viewing side andhas the first and second polarizing films above and below the liquidcrystal cell in a state to cross the transmission axes of the films atan angle nearly perpendicular to each other.

[0032] The positional relationship of the retardation film and thepolarizing film is characterized by the disposition of at least one ofthe retardation film films A and C between the liquid crystal cell andthe first polarizing film and/or between the liquid crystal cell and thesecond polarizing film Examples of concrete arrangement are shown in theFIGS. 1 to 6.

[0033] The retardation film A is preferably placed adjacent to the firstor the second polarizing film for effectively compensating the apparentdeviation of the axes of the polarizing films. The retardation film C ispreferably placed adjacent to the liquid crystal cell for effectivelycompensating the thickness-direction retardation of the liquid crystalcell. The term “adjacent to” used in the present invention means thatboth components are directly contacting with each other by pasting forexample with an adhesive agent.

[0034] Preferably, the slow axis of the retardation films A and/or C isplaced essentially parallel or perpendicular to the polarizing axis ofthe 1st and/or 2nd polarizing films to suppress the impartment ofretardation on the polarized light entering from the front. A pair ofother retardation films having nearly equal characteristics (forexample, a λ/4 plate) may be placed between the liquid crystal cell andthe 1st polarizing film and between the liquid crystal cell and the 2ndpolarizing film in a manner to direct the slow axis of the retardationfilms essentially parallel or perpendicular to each other.

[0035] It is preferable that the retardation films A and C have in-planeretardations at 550 nm wavelength (hereinafter referred to as R(550)) of300 nm or under and K(550) values of 400 nm or under, however, theoptimum values are dependent upon the average refractive indices(hereinafter referred to as “n”) of the retardation films A and C andthe combination and arrangement of the retardation films A and C.

[0036] In the present invention, the in-plane retardation R(λ) and thethickness direction retardation K(λ) of the retardation film areexpressed by the following formulas (12) and (13), respectively.

R=(n _(x) −n _(y))×d   (12)

K={(n _(x) +n _(y))/2−n _(z) }×d   (13)

[0037] in the formulas, n_(x), n_(y) and n_(z) are each athree-dimensional refractive index of the retardation film correspondingto the refractive indices in the x axis and y axis in the film plane andthe z axis perpendicular to the film, respectively, and d is thethickness (nm) of the retardation film. λ is wavelength of from 400 to700 nm.

[0038] Namely, the terms n_(x), n_(y) and n_(z) are indices showing theoptical anisotropy of a retardation film. Especially in the case of theretardation film of the present invention,

[0039] n_(x): the maximum refractive index in the film plane,

[0040] n_(y): the refractive index in the direction perpendicular to thedirection of the maximum refractive index in the film plane.

[0041] n_(z): the refractive index in the direction of the normal lineof the film.

[0042] The optically anisotropy is defined to be positive when therefractive index is maximum in the drawing direction in the case ofuniaxial drawing of a polymer film or in the drawing direction to gethigher increase of the orientation degree in the case of biaxialdrawing, i.e. the orientation direction of the polymer main chain fromthe viewpoint of chemical structure, and is defined to be negative whenthe above refractive index in the drawing direction becomes minimum. Thethree-dimensional refractive index is measured in the present inventionby a method to assume the optical anisotropy of the retardation film asan optical indicatrix and determine the three-dimensional refractiveindex by a known formula of optical indicatrix. The three-dimensionalrefractive index depends upon the wavelength of the light source for themeasurement and, accordingly, it is preferable to be defined at thewavelength of the light source. The retardation films are classified inthe present invention by the optical characteristics and called asfollows.

[0043] Retardation film A: n_(x)>n_(y)=n_(z)

[0044] Retardation film C: n_(x)≧n_(y)>n_(z).

[0045] At least two retardation films, namely the retardation film A andthe retardation film C are used in combination in the present invention.The retardation film A has a retardation essentially decreasing withshorter wavelength of the light for measurement and, on the contrary,the retardation of the retardation film C essentially increases with theshortening of the wavelength the light for measurement.

[0046] The above problems can be solved by the combination of such twospecific kinds of retardation films and the reason is supposed asfollows. The retardation film A mainly compensates the apparentdeviation of the axis of the polarizing plate and the retardation film Ccompensates the retardation in the thickness direction generatingbetween a pair of polarizing films. It is preferable to apply an equalangle of retardation (deg) to the polarized light independent of thewavelength for compensating the apparent deviation of the axis of thepolarizing plate over a wide wavelength range. In other words, theretardation becomes smaller at the shorter wavelength when theretardation is expressed by nm. On the other hand, the retardation filmpreferably has the wavelength dispersion of retardation similar to thatof the VA cell in order to compensate the retardation in the thicknessdirection generating between a pair of polarizing films over a widewavelength range. A TAC film having optical anisotropy, etc., ispractically used as a protecting layer of a polarizing film in additionto the VA liquid cell between a pair of polarizing films, however, thethickness direction retardation of the VA liquid crystal cell issufficiently large compared the protecting layer. Accordingly, it ispreferable that the retardation film has a wavelength dispersion ofretardation similar to that of the VA cell, i.e. a retardationincreasing with decreasing wavelength, for compensating the thicknessdirection retardation between a pair of polarizing films over a widewavelength range.

[0047] Accordingly, the retardation film A has a wavelength dispersioncharacteristics of the retardation satisfying the following formulas (1)and/or (2) preferably in single layer.

R(λ₁)/R(λ₂)<1   (1)

K(λ₁)/K(λ₂)<1   (2)

[0048] In other words, retardations (R,K) of the film in the planeand/or thickness direction of the retardation film become smaller atshorter wavelength. It is necessary for the improvement of the viewangle characteristics to use the retardation film A composed essentiallyof a single layer, i.e. a single film without laminating a plurality ofretardation films other than the retardation film A for satisfying theabove requirements and the use of a single film is advantageous from theview point of cost and productivity. As to be mentioned later, theretardation film A may contain a small amount of a liquid crystal forslightly controlling the above characteristics.

[0049] In the above formulas, λ₁ and λ₂ are arbitrary wavelengthssatisfying the following formula (14)

400 nm<λ₁<λ₂<700 nm   (14)

[0050] The retardation film A preferably satisfies the followingformulas (1-1) and/or (1-2).

R(450)/R(550)<1   (1-1)

K(450)/K(550)<1   (1-2)

[0051] The compensation over a wide wavelength is made to be possible bythe use of a retardation film A having a wavelength dispersioncharacteristics satisfying the following formulas (5) and/or (6).

1<R(650)/R(550)   (5)

1<K(650)/K(550)   (6)

[0052] The definitions of R and K are same as those mentioned above.

[0053] The retardation film A preferably further has a wavelengthdispersion characteristics satisfying the following formulas (10) and(11)

0.6<R(450)/R(550)<0.97   (10)

1.01<R(650)/R(550)<1.4   (11)

[0054] and the compensation of the apparent deviation of axis of thepolarizing plate can be improved by setting the retardation ratio to becloser to the ratio of the wavelengths for measurement.

[0055] The retardation film A preferably satisfies the following formula(7).

10<R(550)<300   (7)

[0056] The retardation film C to be used in the present inventionsatisfies the following formulas (3) and (4) (preferably the formulas(4-1) and/or (4-2)) at the same time.

n_(x)≧n_(y)>n_(z)   (3)

1<K(λ₁)/K(λ₂)   (4)

K(650)/K(550)<1   (4-1)

1<K(450)/K(550)   (4-2)

[0057] Namely, the retardation film C is usually a biaxially drawn filmhaving a refractive index n_(z) in the thickness direction of the filmsmallest among the refractive indices. It has larger retardation K inthickness direction at shorter wavelength.

[0058] The retardation film C preferably satisfies the following formula(8) to effectively compensate the retardation in thickness direction ofthe liquid crystal cell.

50<K(550)<400   (8)

[0059] Furthermore, the retardation film C preferably satisfies thefollowing formula (9) to prevent the hindering of the effect of the filmA compensating the deviation of the axis of the polarizing plate.

R(550)<30   (9)

[0060] Especially in the present invention, the use of the retardationfilm A satisfying the above formula (7) and the retardation film Csatisfying the above formula (8) is suitable for the compensation of thedeviation of the axis of the polarizing plate and the compensation ofthe retardation in the thickness direction of the liquid crystal cell.

[0061] When each of the 1st and the 2nd polarizing films in the liquidcrystal display device of the present invention are composed of apolarizing device having protecting layers on both sides as mentionedlater, the above retardation films A and C are preferably used to givethe sum of the thickness-direction retardations of one side of theprotection layers, the retardation films A and C and the liquid crystalcell of from −200 to +200 nm. When other retardation films are used inaddition to the retardation films A and C, the retardation films A and Care preferably used to get the sum of thickness-direction retardationsincluding these additional retardation films of from −200 to +200 nm.

[0062] The retardation film A to be used in the present invention ise.g. the one described in the specification of WO 00/26705(corresponding- to the specification of EP 1045261).

[0063] Concretely, an oriented polymer film satisfying the followingconditions (a) or (b) can be used as the retardation film A.

[0064] (a) An oriented polymer film satisfying the requirements of (1)composed of a polymer containing a monomer unit of a polymer havingpositive refractive index anisotropy (hereinafter referred to as thefirst monomer unit) and a monomer unit of a polymer having negativerefractive index anisotropy (hereinafter referred to as the secondmonomer unit), (2) having the R(450)/R(550) ratio of the polymer derivedfrom the first monomer unit smaller than the R(450)/R(550) ratio of thepolymer derived from the second monomer unit and (3) having positiverefractive index anisotropy, and

[0065] (b) an oriented polymer film satisfying the requirements of (1)composed of a polymer containing a monomer unit forming a polymer havingpositive refractive index anisotropy (hereinafter referred to as thefirst monomer unit) and a monomer unit forming a polymer having negativerefractive index anisotropy (hereinafter referred to as the secondmonomer unit), (2) having the R(450)/R(550) ratio of the polymer derivedfrom the first monomer unit larger than the R(450)/R(550) ratio of thepolymer derived from the second monomer unit and (3) having negativerefractive index anisotropy.

[0066] Examples of the films satisfying the conditions of (a) or (b) arethose satisfying the following conditions (c) or (d).

[0067] (c) An oriented polymer film satisfying the requirements of (1)composed of a polymer blend composed of a polymer having positiverefractive index anisotropy and a polymer having negative refractiveindex anisotropy and/or a copolymer composed of a monomer unit of apolymer having positive refractive index anisotropy and a monomer unitof a polymer having negative refractive index anisotropy, (2) having theR(450)/R(550) ratio of the polymer having positive refractive indexanisotropy smaller than the R(450)/R(550) ratio of the polymer havingnegative refractive index anisotropy and (3) having positive refractiveindex anisotropy, and

[0068] (d) an oriented polymer film satisfying the requirements of (1)composed of a polymer blend composed of a polymer having positiverefractive index anisotropy and a polymer having negative refractiveindex anisotropy and/or a copolymer composed of a monomer unit of apolymer having positive refractive index anisotropy and a monomer unitof a polymer having negative refractive index anisotropy, (2) having theR(450)/R(550) ratio of the polymer having positive refractive indexanisotropy larger than the R(450)/R(550) ratio of the polymer havingnegative refractive index anisotropy and (3) having negative refractiveindex anisotropy.

[0069] The polymer having positive or negative refractive indexanisotropy means a polymer giving an oriented polymer film havingpositive or negative refractive index anisotropy.

[0070] The concrete materials of the oriented polymer film are explainedbelow.

[0071] These polymer materials are often heated in molding and,accordingly, preferable to have excellent heat resistance according tothe use and the glass transition temperature of the material ispreferably 120° C. or above, more preferably 140° C. or above. When theglass transition temperature is lower than 120° C., problems such as therelaxation of orientation may occur according to the use conditions ofthe display element.

[0072] The water absorption of the polymer material is preferably 1% byweight or less. A polymer material having a water absorption exceeding1% by weight may have problems of the change in optical properties orthe dimensional change in the practical use as a retardation film. Thewater absorption of the polymer material is preferably 0.5% by weight orless.

[0073] There is no particular restrictions on the polymer materialconstituting such oriented polymer film, and the preferable materialsare those having excellent heat-resistance and good optical propertiesand formable by solution film-forming method, for example, thermoplasticpolymers such as polyarylates, polyesters, polycarbonates, polyolefins,polyethers, polysulfones and polyether sulfones.

[0074] As mentioned above, the thermoplastic polymer to be used in theabove film is more preferably polymer blends (a mixture of two or morekinds of polymers) composed of a polymer having a positive refractiveindex anisotropy and a polymer having a negative refractive indexanisotropy or a copolymer composed of a monomer unit of a polymer havinga positive refractive index anisotropy and a monomer unit of a polymerhaving a negative refractive index anisotropy. The thermoplastic polymermay be a combination of two or more kinds of polymer blends orcopolymers or a combination of one or more kinds of polymer blends andone or more kinds of copolymers.

[0075] The polymer blend is preferably a compatible blend or a blend ofpolymers having nearly equal refractive indices to attain opticaltransparency. Concrete examples of the combination of polymer blend are,for example, a combination of a poly(methyl methacrylate) as a polymerhaving negative optical anisotropy with at least one kind of polymerselected from poly(vinylidene fluoride), poly(ethylene oxide) andpoly(vinylidene fluoride-co-trifluoroethylene) as a polymer havingpositive optical anisotropy, a combination of a poly(phenylene oxide) asa polymer having positive optical anisotropy with at least one kind ofpolymer selected from polystyrene, poly(styrene-co-lauroylmaleimide),poly(styrene-co-cyclohexylmaleimide) andpoly(styrene-co-phenylmaleimide) as a polymer having negative opticalanisotropy, a combination of a poly(styrene-co-maleic anhydride) havingnegative optical anisotropy with a polycarbonate having positive opticalanisotropy, a combination of a poly(acrylonitrile-co-butadiene) havingpositive optical anisotropy with a poly(acrylonitrile-co-styrene) havingnegative optical anisotropy and a combination of a polycarbonate havingpositive optical anisotropy with a polycarbonate having negative opticalanisotropy, and the present invention is not restricted by the abovecombinations. Especially preferable polymer blend is a blend of apolycarbonate having positive optical anisotropy with a polycarbonatehaving negative optical anisotropy from the viewpoint of transparency.

[0076] Examples of the copolymer are poly(butadiene-co-polystyrene),poly(ethylene-co-polystyrene), poly(acrylonitrile-co-butadiene),poly(acrylonitrile-co-butadiene-co-styrene), polycarbonate copolymers,polyester copolymers, polyester carbonate copolymers and polyarylatecopolymers. Especially preferable copolymers are polycarbonatecopolymers, polyester copolymers, polyester carbonate copolymers,polyarylate copolymers or the like having fluorene skeleton because asegment having fluorene skeleton can impart negative optical anisotropy.

[0077] Among the above examples, polycarbonate copolymers or polymerblends of polycarbonates are especially preferable owing to excellenttransparency, heat-resistance and productivity. The polycarbonate ispreferably an aromatic polycarbonate containing a structure having afluorene skeleton. For example, the polycarbonate contains the recurringunit expressed by the following formula (A).

[0078] In the formula (A), R₁ to R₈ are each independently at least onekind of atom or group selected from hydrogen atom, halogen atoms andhydrocarbon groups having a carbon number of from 1 to 6. Examples ofthe hydrocarbon groups are alkyl groups such as methyl group, ethylgroup, isopropyl group and cyclohexyl group and aryl groups such asphenyl group. Hydrogen atom and methyl group are especially preferableamong the above atoms and groups.

[0079] X is a fluorene group expressed by the following formula.

[0080] The amount of the recurring unit expressed by the above formula(A) is preferably 1 to 99 mol %, more preferably 30 mol % or more basedon the total recurring units.

[0081] The above aromatic polycarbonate is preferably a copolymer and/ora polymer blend composed of 30 to 90 mol % recurring unit (a) expressedby the above formula (A) and 70 to 10 mol % recurring unit (b) expressedby the following formula (B) based on the total recurring units.

[0082] In the above formula (B), R₉ to R₁₆ are each independently anatom or group selected from hydrogen atom, halogen atoms and hydrocarbongroups having a carbon number of from 1 to 22. Examples of thehydrocarbon group having a carbon number of from 1 to 22 are alkylgroups having a carbon number of from 1 to 9 such as methyl group, ethylgroup, isopropyl group and cyclohexyl group or aryl groups such asphenyl group, biphenyl group and terphenyl group. Hydrogen atom andmethyl group are especially preferable among the above atoms and groups.

[0083] The group Y in the above formula (B) is expressed by thefollowing formulas.

[0084] In the formulas, the groups R₁₇ to R₁₈, R₂₁ and R₂₂ are eachindependently selected from hydrogen atom, halogen atoms and hydrocarbongroups having a carbon number of from 1 to 22. Examples of thehydrocarbon groups are same as those cited above. The groups R₂₀ and R₂₃are each independently selected from hydrocarbon groups having a carbonnumber of from 1 to 20 and the examples of the hydrocarbon groups aresame as those cited above. Ar₁ to Ar₃ are each independently an arylgroup having a carbon number of from 6 to 10, such as phenyl group andnaphthyl group.

[0085] The content of the recurring unit of the formula (A) ispreferably from 35 to 85 mol %, more preferably from 45 to 80 mol %based on the total recurring units.

[0086] The content of the recurring unit of the formula (A) is dependentupon the required wavelength dispersion characteristics of retardationespecially when the groups R₁ to R₈ in the formula (A) are hydrogenatoms or a part of the groups are methyl group and the groups R₉ to R₁₆in the formula (B) are hydrogen atoms and Y is isopropylene group. Thelower limit of the content is 45 mol %, preferably 50 mol %, morepreferably 55 mol %. The upper limit is 80 mol %, preferably 75 mol %,more preferably 70 mol %. Especially preferable range of the content isfrom 55 to 70 mol %.

[0087] The above copolymer of the aromatic polycarbonate may be acombination of two or more each of the recurring units of the formula(A) and formula (B) and the polymer blend may be a combination of two ormore each of the above recurring units.

[0088] The molar ratio can be determined on the bulk polycarbonateconstituting the oriented polymer film irrespective of a copolymer or apolymer blend by a nuclear magnetic resonance (NMR) instrument, etc.

[0089] The copolymers and polymer blends can be produced by conventionalmethods. Suitable processes for the production of polycarbonates are thepolycondensation of a dihydroxy compound with phosgene, the meltpolycondensation process, etc. Blending of two or more mutuallycompatible polycarbonates by melt mixing, etc., is preferable in thecase of producing a polymer blend, however, the light scattering betweenthe components can be suppressed to improve the transparency even in ablend of components which are not completely compatible with each otherby setting the refractive indices of the components to coincide witheach other.

[0090] The intrinsic viscosity of the aromatic polycarbonate ispreferably from 0.3 to 2.0 dl/g. When the intrinsic viscosity is smallerthan 0.3, the polymer becomes brittle to lose the mechanical strength. Apolymer having an intrinsic viscosity exceeding 3.0 has problems of thegeneration of die line, etc., in the solution film-forming process andthe difficulty in the purification after the completion ofpolymerization owing to its excessively high solution viscosity.

[0091] Preferably, the retardation film C of the present invention alsohas excellent heat resistance similar to the retardation film A and theglass transition temperature of the polymer material constituting thefilm C is 120° C. or over, preferably 140° C. or over. When the glasstransition temperature is lower than 120° C., problems such as therelaxation of orientation may occur according to the use conditions ofthe display element.

[0092] The water absorption is also preferably 1% by weight or below.

[0093] There is no particular restrictions on the polymer material, andthe examples of the material are thermoplastic polymers such aspolyarylates, polyesters, polycarbonates, polyolefins, polyethers,polysulfones and polyether sulfones.

[0094] Materials having excellent heat resistance and transparency, goodoptical performance and formable by solution film forming process arepreferable among the above examples. Examples of the preferablematerials are aromatic polycarbonates and polyolefins.

[0095] The retardation film of the present invention is preferablytransparent and preferably has a haze value of 3% or less and a totallight transmittance of 85% or above.

[0096] The retardation film of the present invention may be incorporatedwith an ultraviolet absorber such as phenylsalicylic acid,2-hydroxybenzophenone and triphenyl phosphate, a bluing agent to varythe color tone, an antioxidant, etc.

[0097] The retardation film of the present invention is produced byconventional melt-extrusion method, solution casting method, etc. Thesolution casting method is more preferable from the viewpoint of theuniformity of film thickness, the appearance of the film, etc.Concretely, in the case of using a polycarbonate as the polymermaterial, the polycarbonate is dissolved in an organic solvent such asmethylene chloride or dioxolane and an undrawn film is produced bysolution casting method. The produced undrawn film is uniaxially orbiaxially drawn by a conventional method to obtain a retardation filmhaving a desired retardation.

[0098] Examples of the drawing method to form a retardation film A arecontinuous drawing methods such as a longitudinal uniaxial roll drawingmethod to draw a film taking advantage of the speed difference betweenrolls, a longitudinal uniaxial tenter drawing method to hold the lateraledges of a film with pins or clips and drawing the film taking advantageof the difference of the speed of the holding parts of the tenter in theflow direction of the film and a lateral uniaxial tenter drawing methodto expand a tenter in lateral direction, and the longitudinal uniaxialroll drawing method is preferable among the above methods from theviewpoint of the uniformity of the film characteristics, etc.

[0099] Examples of the drawing method for the production of aretardation film C are a consecutive biaxial drawing method to draw thefilm separately in longitudinal and lateral directions by theabove-mentioned uniaxial drawing method, a simultaneous biaxial drawingmethod to laterally expand a tenter having speed difference in the flowdirection of the film, a multi-stage drawing method to repeat the abovedrawing procedure several times.

[0100] Several examples of continuous drawing methods for producing aretardation film were shown above, however, the drawing method of theretardation film of the present invention is not restricted by theexamples. Although continuous drawing is preferable from the viewpointof productivity, the film is not necessarily produced by the continuousdrawing method.

[0101] In the case of drawing the film by a technique represented by theabove drawing methods, the film may be incorporated with a conventionalplasticizers to improve the drawability. Examples of the plasticizersare phthalic acid esters such as dimethyl phthalate, diethyl phthalateand dibutyl phthalate, phosphoric acid esters such as tributylphosphate, aliphatic dibasic acid esters, glycerol derivatives andglycol derivatives. The organic solvent used in the above-mentionedfilm-forming process may be present in the film at the drawing process.The amount of the organic solvent left in the film is preferably 1 to20% by weight based on the solid component of the polymer.

[0102] The above additives such as plasticizers and liquid crystals canvary the wavelength dispersion of the retardation of the retardationfilm and the addition amount of the additive is preferably 10% by weightor less, more preferably 3% by weight or less based on the solidcomponent of the polymer, that is the weight of the polymer materialconstituting the retardation film.

[0103] The thickness of the retardation film of the present invention ispreferably from 1 μm to 300 μm. The expression of retardation film usedin the present invention includes all “films” and “sheets”.

[0104] The retardation film C may be a film produced by fixing a liquidcrystalline polymer on a substrate (a drawn or undrawn film) in orientedstate as well as a film produced by drawing a polymer material. Thesubstrate is preferably the retardation film A from the viewpoint of thefilm thickness.

[0105] As mentioned above, the chemical structure of the polymerconstituting the oriented polymer film is important for decreasing theretardation of a retardation film A at shorter wavelength. Although thewavelength dispersion of retardation is mostly determined by thechemical structure, it is necessary to pay attention to the fact thatthe dispersion is also dependent on the film-forming conditions,additives, drawing conditions, blended state, molecular weight, etc.

[0106] Conventional polarizing films can be used as the polarizing filmof the present invention. Examples of the polarizing film is a filmproduced by dispersing iodine or a dichroic dye, etc., in a polymer(called also as a binder polymer) such as polyvinyl alcohol andorienting and fixing at least the iodine, etc., by the drawing, etc., ofthe film and a film produced by drawing a main chain type or a sidechain type polyacetylene. A polarizing film produced by using apolyvinyl alcohol as the binder polymer is usually laminated with acellulose acetate film, etc., as a protecting film. The polarizing filmmay be used in the form laminated with such protecting film or by usingthe retardation film of the present invention as a substitute for theprotecting film without using the above protecting film.

[0107] The thickness of the polarizing film is usually from 30 to 300 μmfor a film produced by using the above binder polymer. In the case of afilm having a dichroic liquid crystal material oriented and fixed to thefilm by coating, the thickness is about 0.01 to 30 μm.

[0108] The liquid crystal display device of the present invention is acombination of a retardation film, a VA-mode liquid crystal cellcontaining a liquid crystal panel substrate and a polarizing film. Theretardation film and the polarizing film are preferably used in a stateadjacent to each other, namely, closely contacting with each other. Theclose contact of the members can be achieved by using conventionaladhesives.

[0109] A backlight may be placed at the opposite side (back side) of theliquid crystal cell of the liquid crystal display device of the presentinvention. In this case, various optical films such as a prism sheet ora light-scattering film may be placed between the liquid crystal displaydevice and the backlight.

[0110] The present invention can be in a liquid crystal display, aliquid crystal projector, etc., and is extremely useful especially as aliquid crystal display device of vertical aligned mode necessitating awide view angle.

[0111] Preferable examples of the constitution of the liquid crystaldisplay device of the present invention provided with a backlight areshown in the FIG. 1 to FIG. 6, which do not restrict the constitution ofthe present invention.

[0112] Preferably, either one of the polarizing films is placed adjacentto the retardation film as shown in the FIGS. 1 to 4;

[0113] In these examples, the retardation film A may be used as a singlesheet or as a laminate of a plurality of the retardation films A.Similarly, the film C may be replaced with a laminate of a plurality ofthe films C. In the case of laminating a plurality of films, thedirections of the retardation films having the largest refractive index,that is, the directions of the optical axes are preferably aligned.Furthermore, the element may be a reflection type or semi-transmittingreflection type liquid crystal display device having a reflection plateor a semi-transmitting reflection plate as the backlight and thepolarizing film of the backlight side.

[0114] The preferable embodiment of the present invention is describedbelow.

[0115] The preferable embodiment of the present invention is a liquidcrystal display device composed of a liquid crystal cell holding a VAliquid crystal between a pair of substrates in a state directing themajor axis of the liquid crystal molecule nearly perpendicular to thesubstrate face in the absence of voltage, a 1st and a 2nd polarizingfilms placed at both sides of the liquid crystal cell and havingpolarizing axes nearly perpendicular to each other and at least tworetardation films (A,C) placed between the liquid crystal cell and thepolarizing films, wherein the retardation film A satisfies the followingformula (10) and/or (11) in the form of a single sheet

0.6<R(450)/R(550)<0.97   (10)

1.01<R(650)/R(550)<1.4   (11),

[0116] the retardation film C satisfies the following formula (3) andformulas (4-1) and/or (4-2)

n_(x)≧n_(y)>n_(z)   (3)

K(650)/K(550)<1   (4-1)

1<K(450)/K(550)   (4-2),

[0117] the retardation film A is placed adjacent to the 1st polarizingfilm or the 2nd polarizing film, the retardation film C is placedadjacent to the liquid crystal cell, the slow axis of the retardationfilm A is placed parallel or perpendicular to the polarizing axis of the1st polarizing film, the retardation film A satisfies the followingformula (7)

10<R(550)<300   (7),

[0118] the retardation film C satisfies the following formula (8)

50<K(550)<400   (8)

[0119] and the formula (9)

R(550)<30   (9)

[0120] and the retardation film A contains a polycarbonate having afluorene skeleton. The definitions of R, K, n_(x), n_(y) and n_(z) inthe above formulas are same as those described above.

[0121] Accordingly, it has been cleared by the present invention that aliquid crystal display device of VA mode having decreased leakage oflight over the whole visible light range and giving a clear and almostachromatic black display can be produced by using the retardation film Ain combination with the retardation film C of the present invention.

[0122] The present invention provides a method for compensating the viewangle of a liquid crystal display device over the whole visible lightrange by providing a liquid crystal cell holding a liquid crystalbetween a pair of substrates in a state directing the major axis of theliquid crystal molecule nearly perpendicular to the substrate face inthe absence of voltage, a 1st and a 2nd polarizing films placed at bothsides of the liquid crystal cell and having polarizing axes nearlyperpendicular to each other and at least two retardation films (A,C)placed between the liquid crystal cell and the 1st and 2nd polarizingfilms, wherein the polarizing film A satisfies the following formula (1)and/or (2)

R(λ₁)/R(λ₂)<1   (1)

K(λ₁)/K(λ₂)<1   (2)

[0123] and the retardation film C satisfies the following formulas (3)and (4) at the same time.

n_(x)≧n_(y)>n_(z)   (3)

1<K(λ₁)/K(λ₂)   (4)

[0124] In the above formulas (1) and (2), R(λ₁) and R(λ₂) are each anin-plane retardation or the retardation film at wavelength of λ₁ and λ₂,K(λ₁) and K(λ₂) are each a thickness-direction retardation of theretardation film at wavelength of λ₁ and λ₂ and λ₁ and λ₂ arewavelengths satisfying the formula 400 nm<λ₁<λ₂<700 nm.

[0125] The term n_(x) is the maximum refractive index in the film plane,n_(y) is the refractive index in the direction perpendicular to thedirection of the maximum refractive index in the film plane and n_(z) isthe refractive index in the direction of the normal line of the film.The definitions of K, λ₁ and λ₂ are same as those described above.

[0126] The present method, i.e. the concrete method for applying theabove retardation film A and the retardation film C to a liquid crystaldisplay device of VA mode will be apparent from the above explanations.

[0127] The present invention further provides a combination of theretardation film A satisfying the following formula (1) and/or formula(2)

R(λ₁)/R(λ₂)<1   (1)

K(λ₁)/K(λ₂)<1   (2)

[0128] with the retardation film C satisfying the following formulas (3)and (4)

n_(x)≧n_(y)>n_(z)   (3)

1<K(λ₁)/K(λ₂)   (4)

[0129] for the use as a retardation film (viewing angle compensationfilm) of a liquid crystal display device of VA mode.

[0130] The definitions of R, K, n_(x), n_(y) and n_(z) in the formulasare same as those described above.

[0131] The use of the films, i.e. the concrete use for applying theabove retardation film A and the retardation film C to a liquid crystaldisplay device of VA mode will be apparent from the above explanations.

EFFECT OF THE INVENTION

[0132] As described above, the present invention can provide a VA modeliquid crystal display device causing decreased leakage of light overthe whole visible light range and enabling the display of a clear andnearly achromatic black color by combining a retardation film A havingsmaller retardation at shorter wavelength with a retardation film Chaving larger retardation at shorter wavelength. Accordingly, the viewangle can be widened over the whole visible light range.

EXAMPLES

[0133] The present invention is explained in more detail by thefollowing examples, which do not restrict the scope of the presentinvention.

[0134] (Evaluation Methods)

[0135] The properties, etc., of the materials described in thespecification were determined by the following evaluation methods.

[0136] (1) Determination of Retardation R in In-Plane Direction andRetardation K in Thickness Direction

[0137] The retardation R in in-plane direction and the retardation K inthickness direction were determined by the Spectroscopic Ellipsometer“M150” (product of JASCO Corp.). The R value was measured in a state tocross the incident light with the film surface at right angle. The Kvalue was determined by measuring the retardation values at variousangles by varying the angle between the incident light and the filmsurface and determining the three-dimensional refractive indices n_(x),n_(y) and n_(z) by the curve fitting with a known formula of refractiveindex ellipsoid. The average refractive index n necessary as anotherparameter in the above procedure is measured by an Abbe refractometer(Abbe Refractometer 2-T product of ATAGO Co., Ltd.).

[0138] (2) Determination of Water Absorption

[0139] The water absorption was determined in conformity with the“Determination of Water Absorption and Boiling Water Absorption ofPlastics” described in JIS K 7209 except for the use of a film having afilm thickness of 130±50 μm in dried state. The size of the test piecewas 50 mm square. The sample was immersed in water at 25° C. for 24hours and the variation of the weight was measured. The result wasexpressed by % by weight.

[0140] (3) Determination of the Glass Transition Temperature (Tg) of thePolymer

[0141] The glass transition temperature was measured by “DSC2920Modulated DSC” (product of TA Instruments). The measurement was carriedout not on a film but in the form of flakes or chips after theproduction of the polymer.

[0142] (4) Determination of the Film Thickness

[0143] The thickness of the film was measured by an electronicmicrometer manufactured by Anritsu Corp.

[0144] (5) Determination of the Copolymerization Ratio of the Polymer

[0145] The copolymerization ratio was measured by a proton NMR“JNM-alpha600” (product of JEOL Ltd.). Especially in the case of acopolymer of bisphenol A and biscresol fluorene, deuterobenzene was usedas the solvent and the ratio was calculated from the proton intensityratio of each methyl group.

[0146] (6) Polymerization of Polycarbonate Copolymer

[0147] The monomer structures for the production of the polycarbonateused in the Examples are shown below.

[0148] An aqueous solution of sodium hydroxide and ion-exchanged waterwere charged in a reactor furnished with a stirrer, a thermometer and areflux condenser, the monomers X and Y having the above structures weredissolved in the solution at a molar ratio of 33:67 and a small amountof hydrosulfite was added to the system. Methylene chloride was addedthereto and phosgene was blown into the reactor at 20° C. spending about60 minutes. The content of the reactor was emulsified by addingp-tert-butylphenol, triethylamine was added to the emulsion and theproduct was stirred at 30° C. for about 3 hours to complete thereaction. After the completion of the reaction, the organic phase wascollected and methylene chloride was evaporated to obtain apolycarbonate copolymer. The compositional ratio of the obtainedcopolymer was nearly equal to the charging ratio of the monomers.

Example 1

[0149] The polycarbonate copolymer produced by the above method wasdissolved in methylene chloride to obtain a dope solution having a solidconcentration of 18% by weight. A cast film was prepared from the dopesolution on a substrate by solution casting method. The film was peeledoff from the substrate and dried by slowly raising the temperature toTg-20° C. The produced dried film was uniaxially drawn at 230° C. at adraw ratio of 1.6 to obtain a film A (copolymer PC1). It has beenconfirmed that the film has smaller retardation at shorter wavelengthfor measurement and has positive refractive index anisotropy.

[0150] ARTON manufactured by JSR Ltd. was dissolved in methylenechloride to produce a dope solution having a solid concentration of 18%by weight. A cast film was prepared from the dope solution by a methodsimilar to the method described above and biaxially drawn at 175° C. atdraw ratios of 1.3 in longitudinal and lateral directions to obtain aretardation film C (ARTON1). The film was confirmed to have largerretardation at shorter wavelength for measurement.

[0151] A VA liquid crystal cell having the characteristics shown in thefollowing Table 1 was prepared and laminated with a commerciallyavailable iodine-type polarizing film (HLC2-5618, product of SanritzCorp.) and the above retardation film with an adhesive to form theconstitution shown in the following Table 2. There was little leakage oflight by viewing the obtained panel in slant direction at any angle andthe leaked light was colorless. TABLE 1 n (550) 1.504 d (μm) 4 R (450)(nm) 0 R (550) (nm) 0 R (650) (nm) 0 K (450) (nm) −325 K (550) (nm) −310K (650) (nm) −305

[0152] TABLE 2 Comparative Example 1 Example 2 Example 1 1st PolarizingFilm 1st Polarizing Film 1st Polarizing Film (Transmission axis(Transmission axis (Transmission axis 90°) 90°) 90°) PC copolymer 1 PCcopolymer 2 ARTON2 (Slow axis 90°) (Slow axis 90°) (Slow axis 90°)Liquid crystal cell Liquid crystal cell Liquid crystal cell ARTON1 PC1ARTON3 2nd Polarizing Film 2nd Polarizing Film 2nd Polarizing Film(Transmission axis 0°) (Transmission axis 0°) (Transmission axis 0°)Backlight Backlight Backlight

Example 2

[0153] A bisphenol A polycarbonate (C1400; product of Teijin ChemicalsLtd.) was dissolved in methylene chloride to obtain a dope solutionhaving a solid concentration of 18% by weight. A cast film was preparedfrom the dope solution by a method similar to the Example 1. The filmwas biaxially drawn at 165° C. at draw ratios of 1.1 in longitudinal andlateral directions to obtain a retardation film C (PC1). The film wasconfirmed to have larger retardation at shorter wavelength formeasurement.

[0154] A panel constitution similar to that of the Example 1 except forthe use of PC1 in place of ARTON1 was prepared. There was little leakageof light by viewing the obtained panel in slant direction at any angleto develop a nearly complete black color and the leaked light wascolorless.

Comparative Example 1

[0155] ARTON (product of JSR) was dissolved in methylene chloride toobtain a dope solution having a solid concentration of 18% by. weight. Acast film was prepared from the dope solution and uniaxially drawn at175° C. at a draw ratio of 1.4 to obtain a film A (ARTON2). Separately,the cast film was biaxially drawn at 175° C. at draw ratios of 1.3 inlongitudinal and lateral directions to obtain a film C (ARTON3).

[0156] A panel constitution shown in the Table 2 was produced by usingthese films. The leakage of light was confirmed especially by viewingthe panel from slant direction at an angle of 45° and the leaked lighthad a colored black color.

[0157] The optical characteristics of the retardation films used in theExamples and the Comparative Example are shown in the following Table 3.TABLE 3 PC copolymer 1 ARTON 1 PC1 ARTON 2 ARTON 3 n (550) 1.6240 1.51751.5875 1.5175 1.5175 R (450) (nm) 123 0 0 141 0 R (550) (nm) 150 0 0 1400 R (650) (nm) 159 0 0 140 0 K (450) (nm) 62 222 270 71 212 K (550) (nm)75 220 250 70 210 K (650) (nm) 80 219 245 70 209 nx (550) 1.6250 1.51821.5883 1.5184 1.5182 ny (550) 1.6235 1.5182 1.5883 1.5170 1.5182 nz(550) 1.6235 1.5160 1.5858 1.5170 1.5161 Film 90 150 80 80 150 thicknessafter drawing Glass 225 170 160 170 170 transition temperature (° C.)Water 0.2 0.2 0.2 0.2 0.2 absorption (wt. %)

INDUSTRIAL APPLICABILITY

[0158] The present invention provides a liquid crystal display device ofVA mode having decreased leakage of light over a wide range anddisplaying clear and almost achromatic black color by using at least tworetardation films by combining a retardation film A having smallerretardation with shorter wavelength with a retardation film C havinglarger retardation with shorter wavelength. Accordingly, such liquidcrystal display device can provide a high-quality liquid crystal displaydevice having excellent picture quality.

1. A liquid crystal display device composed of a liquid crystal cellcontaining a liquid crystal held between a pair of substrates in a stateto orient a major axis of a liquid crystal molecule in a directionnearly perpendicular to the face of the substrate in the absence ofapplied voltage, a 1st and a 2nd polarizing films placed at both sidesof the liquid crystal cell and having polarizing axes directingperpendicular to each other and at least two retardation films (A,C)placed between the liquid crystal cell and the polarizing films whereinthe retardation film A satisfies the following formula (1) and/or (2)R(λ₁)/R(λ₂)<1   (1) K(λ₁)/K(λ₂)<1   (2) (in the formulas (1) and (2),R(λ₁) and R(λ₂) are each an in-plane retardation at wavelength of λ₁ andλ₂, K(λ₁) and K(λ₂) are each a retardation of the retardation film inthe direction of thickness at wavelength of λ₁ and λ₂, and λ₁ and λ₂ arewavelengths satisfying the relationship of 400 nm<λ₁<λ₂<700 nm), and theretardation film C satisfies the following formulas (3) and (4) at thesame time. n_(x)≧n_(y)>n_(z)   (3) 1<K(λ₁)/K(λ₂)   (4) (in the formulas,n_(x) is a maximum refractive index in a plane of the retardation film,n_(y) is a refractive index in a direction perpendicular to thedirection of the maximum refractive index in the plane of theretardation film and n_(z) is a refractive index in the normal linedirection of the retardation film, and the definitions of k, λ₁ and λ₂are same as those described above):
 2. A liquid crystal display deviceaccording to claim 1 wherein the retardation film A is placed adjacentto the 1st or the 2nd polarizing film.
 3. A liquid crystal displaydevice according to claim 1 wherein the retardation film C is placedadjacent to the liquid crystal cell.
 4. A liquid crystal display deviceaccording to claim 1 wherein a slow axis of the retardation film A isparallel or perpendicular to the polarization axis of the polarizingfilm.
 5. A liquid crystal display device according to claim 1 whereinthe wavelength λ₁ is 450 nm and λ₂ is 550 nm.
 6. A liquid crystaldisplay device according to claim 1 wherein the retardation film Asatisfies the following formula (5) and/or (6) 1<R(650)/R(550)   (5)1<K(650)/K(550)   (6) (in the formulas, R(650) and R(550) are thein-plane retardance of the retardation film at wavelengths of 650 nm and550 nm, respectively, and K(650) and K(550) are the retardance of theretardation film in the direction of thickness at wavelengths of 650 nmand 550 nm, respectively).
 7. A liquid crystal display device accordingto claim 1 wherein the retardation film C satisfies the followingformula (4-1) K(650)/K(550)<1   (4-1) (in the formula, the definitionsof R and K are same as those described above).
 8. A liquid crystaldisplay device according to claim 1 wherein the retardation film Asatisfies the following formula (7) 10<R(550)<300   (7) and theretardation film C satisfies the following formula (8) 50<K(550)<400  (8) (in the formula, the definitions of R and K are same as thosedescribed above).
 9. A liquid crystal display device according to claim1 wherein both of the retardation films A and C are made of a polymermaterial having a water absorption of 1% by weight or less.
 10. A liquidcrystal display device according to claim 1 wherein the retardation filmA is composed of a single layer.
 11. A liquid crystal display deviceaccording to claim 1 wherein the retardation film A is composed of anoriented polymer film composed of a monomer unit of a polymer havingpositive refractive index anisotropy and a monomer unit of a polymerhaving negative refractive index anisotropy.
 12. A liquid crystaldisplay device according to claim 11 wherein the retardation film Acomprises a polycarbonate having a fluorene skeleton.
 13. A liquidcrystal display device according to claim 1 wherein the retardation filmC satisfies the following formula (9) R(550)<30   (9) (in the formula,the definition of R is same as that described above).
 14. A liquidcrystal display device according to claim 1 provided that, when both ofthe 1st and the 2nd polarizing films are composed of polarizing deviceshaving protective layers on both sides, the sum of the retardations ofone of the protecting layers, the retardation films A and C and theliquid crystal cell in the thickness direction at wavelength of 550 nmis from −200 nm to +200 nm.
 15. A liquid crystal display device composedof a liquid crystal cell containing a liquid crystal held between a pairof substrates in a state to orient a major axis of a liquid crystalmolecule in a direction nearly perpendicular to the face of thesubstrate in the absence of applied voltage, a 1st and a 2nd polarizingfilms placed at both sides of the liquid crystal cell and havingpolarizing axes directing perpendicular to each other and at least tworetardation films (A,C) placed between the liquid crystal cell and thepolarizing films wherein the retardation film A satisfies the followingformulas (10) and (11) in a state of a single sheet,0.6<R(450)/R(550)<0.97   (10) 1.01<R(650)/R(550)<1.4   (11) theretardation film C satisfies the following formula (3) and {(4-1) and/or(4-2)} at the same time, n_(x)≧n_(y)>n_(z)   (3) K(650)/K(550)<1   (4-1)1<K(450)/K(550)   (4-2) the retardation film A is placed adjacent to the1st polarizing film or the 2nd polarizing film, the retardation film Cis placed adjacent to the liquid crystal cell, a slow axis of theretardation film A is parallel or perpendicular to the polarizing axisof the 1st polarizing film, the retardation film A satisfies thefollowing formula (7), 10<R(550)<300   (7) the retardation film Csatisfies the following formula (8), 50<K(550)<400   (8) and satisfiesthe following formula (9), R(550)<30   (9) (in the formulas, thedefinitions of R, K, n_(x), n_(y) and n_(z) are same as those describedabove, R(450) is an in-plane retardation of the retardation film at 550nm and R(550) is retardation in thickness direction at 450 nmwavelength, and the retardation film A comprises a polycarbonate havinga fluorene skeleton).
 16. A liquid crystal display device composed of aliquid crystal cell containing a liquid crystal held between a pair ofsubstrates in a state to orient a major axis of a liquid crystalmolecule in a direction nearly perpendicular to the face of thesubstrate in the absence of applied voltage, a 1st and a 2nd polarizingfilms placed at both sides of the liquid crystal cell and havingpolarizing axes directing perpendicular to each other and at least tworetardation films (A,C) placed between the liquid crystal cell and thepolarizing films wherein the retardation film A has essentially largerretardation in the direction of plane and/or thickness of the film atshorter wavelength within the wavelength range of from 400 nm to 700 nm,and the retardation film C has essentially smaller retardation inthickness direction at shorter wavelength and satisfies the followingformula (3) n_(x)≧n_(y)>n_(z)   (3) (in the formula, the definitions ofn_(x), n_(y) and n_(z) are same as those described above).
 17. A methodfor compensating the view angle of a liquid crystal display device in awhole visible light range by providing a liquid crystal cell containinga liquid crystal held between a pair of substrates in a state to orienta major axis of the liquid crystal molecule in a direction nearlyperpendicular to the face of the substrate in the absence of appliedvoltage, a 1st and a 2nd polarizing films placed at both sides of theliquid crystal cell and having polarizing axes directing perpendicularto each other and at least two retardation films (A,C) placed betweenthe liquid crystal cell and the polarizing films wherein the retardationfilm A satisfies the following formula (1) and/or (2) R(λ₁)/R(λ₂)<1  (1) K(λ₁)/K(λ₂)<1   (2) (in the formulas (1) and (2), R(λ₁) and R(λ₂)are each an in-plane retardation of the retardation film at wavelengthof λ₁ and λ₂, K(λ₁) and K(λ₂) are each a retardation in the direction ofthe thickness of the retardation film at wavelength of λ₁ and λ₂, and λ₁and λ₂ are wavelengths satisfying the relationship of 400 nm<λ₁<λ₂<700nm), and the retardation film C satisfies the following formulas (3) and(4) at the same time. n_(x)≧n_(y)>n_(z)   (3) 1<K(λ₁)/K(λ₂)   (4) (inthe formulas, n_(x) is a maximum refractive index in the plane of theretardation film, n_(y) is a refractive index in the directionperpendicular to the direction of the maximum refractive index in theplane of the retardation film and n_(z) is a refractive index in thenormal line direction of the retardation film, and the definitions of K,λ₁ and λ₂ are same as those described above).
 18. The use of aretardation film A satisfying the following formula (1) and/or (2)R(λ₁)/R(λ₂)<1   (1) K(λ₁)/K(λ₂)<1   (2) in combination with aretardation film C satisfying the following formulas (3) and (4)n_(x)≧n_(y)>n_(z)   (3) 1<K(λ₁)/K(λ₂)   (4) (in the formulas, thedefinitions of R, K, λ₁, λ₂, n_(x), n_(y) and n_(z) are same as thosedescribed above) as a view angle compensation film of a liquid crystaldisplay device of VA mode.